What to know about a rapidly rising form of breast cancer that’s hard to detect

By Faye Chiu, CNN

Rates of one type of breast cancer — invasive lobular carcinoma — have been rising in the United States more than three times faster than those of all other breast cancers combined over the past decade, according to a new study.

This elusive breast cancer that’s hard to spot in routine mammograms is behind more than 1 in 10 cases nationwide.

The research, published in Cancer, the journal of the American Cancer Society, analyzed national data from 2012 to 2021 and found that rates of invasive lobular carcinoma increased by about 2.8% each year, while rates of all other breast cancer rose by about 0.8% a year.

What exactly is invasive lobular carcinoma, and how common is it? How is it diagnosed, and why can it be more difficult to find during screenings? Who is most at risk? What are the treatment options? And what should women know about reducing their risk of developing this and other types of breast cancer?

To help us with these questions, I spoke with CNN wellness medical expert Dr. Leana Wen, an emergency physician and adjunct associate professor at the George Washington University. Wen previously served as Baltimore’s health commissioner.

CNN: What is invasive lobular carcinoma, and how common is it?

Dr. Leana Wen: Invasive lobular carcinoma, also known as ILC or lobular breast cancer, is a type of breast cancer that begins in the milk-producing glands of the breast, called lobules, and then spreads into nearby tissue. These malignant tumors are often hormone receptor-positive, meaning the cancer cells grow in response to estrogen or progesterone.

ILC is the second most common type of breast cancer, after invasive ductal carcinoma, and accounts for 10% to 15% of all new breast cancer diagnoses, according to the National Cancer Institute. About 47,500 ILC cases are diagnosed in the US each year, and more women are diagnosed with it than with brain, kidney, liver, pancreatic or ovarian cancer.

CNN: Why is ILC often more difficult to find with routine mammograms?

Wen: This type of tumor tends to grow in a way that doesn’t change the breast’s structure as much as other cancers. Instead of forming a defined mass, the cancer cells spread through the tissue in thin strands that appear more like normal breast tissue on imaging. Because of this, mammograms may show only subtle changes, or sometimes none at all. Women may also be less likely to feel a distinct lump during a breast self-exam, which can delay detection.

CNN: What other imaging is used to diagnose ILC?

Wen: A breast ultrasound can help spot areas of thickened tissue that don’t show up on a mammogram, and a breast MRI provides a more detailed view that can reveal cancers hidden in dense breast tissue.

These tests aren’t routinely recommended for everyone. Mammography remains the standard screening tool for most women. But those at higher risk, including women with dense breasts and those with a strong family history of breast cancer or known genetic mutations, may be advised to have an ultrasound or MRI in addition to regular mammograms.

CNN: What does this study show in terms of the rise of cases and who is most at risk?

Wen: Researchers found that ILC has been increasing across every racial and ethnic group, but the steepest rise was seen among Asian American and Pacific Islander women, whose incidence grew by about 4.4% each year in the study period. Age is also a risk factor, as women 65 and older are more likely to be diagnosed with ILC than with invasive ductal carcinoma. About 70% of new ILC cases were diagnosed in women 60 and older; the median age of diagnosis is 66.

CNN: How do the study authors explain the rise especially in this type of breast cancer?

Wen: Several factors may be driving this greater increase. Because ILC is strongly linked to hormones, changes in hormone exposure over time could be part of the reason. Rising rates of obesity and alcohol use, along with changes in childbearing and menopause patterns, may also contribute to the steady increase.

Improvement in diagnosis and greater awareness of ILC may be leading to more accurate identification. Some lobular cancers may have been misclassified as ductal cancers in the past, so part of the rise may reflect better recognition. In addition, more women are living longer after menopause, which can increase the likelihood of developing ILC compared with other types of breast cancer.

CNN: What are the treatment options for ILC?

Wen: Treatment is similar to that for other breast cancers. Surgery to remove the tumor, followed by radiation, is common, as is hormonal therapy, since most tumors grow in response to estrogen or progesterone. Chemotherapy may be used in some cases. For advanced disease, newer targeted drugs combined with hormonal therapy can help slow progression and improve outcomes. However, ILC may have greater resistance to treatment, especially in more advanced disease, and tends to carry a poorer prognosis once it has spread.

CNN: How can women reduce their risk of developing ILC and other types of breast cancer?

Wen: Some risk factors can’t be changed, such as age or family history, but many lifestyle choices can make a difference. Quitting smoking, limiting alcohol, maintaining a healthy weight and staying physically active all help lower the risk of breast cancer. Eating a balanced diet rich in fruits, vegetables and whole grains supports overall health and may reduce inflammation linked to cancer.

Regular screening and knowing what’s normal for your breasts are key for early detection. Talk with your doctor about your risk factors and decide together when you should begin screening and whether you need tests in addition to a mammogram.

Finally, pay attention to changes in your breasts, such as thickening, swelling, nipple discharge, different colors or new areas of fullness, and seek medical evaluation as soon as something looks or feels different.

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